A piezoelectric-electromagnetic hybrid energy harvester with frequency-up conversion mechanism towards low-frequency-low-intensity applications

This paper proposes a piezoelectric-electromagnetic hybrid energy harvester (PEHEH) with frequency-up conversion (FUC) mechanisms toward harvesting low-frequency-low-intensity, and wideband vibrational energy. The PEHEH consists of a stator with embedded coils, an eccentric rotor embedded with permanent magnets, and a fan-folded piezoelectric beam fixed to the stator. The eccentric rotor converts low-frequency straight vibration into rotational motion, and generates currents across the coils. The rotor could collide with the fan-folded beam, resulting in voltage generation due to the deformation of the fan-folded beam. The FUC mechanism broadens the bandwidth and harvests additional energy through the piezoelectric effect. The fan-folded beam can be considered as a nonlinear oscillator of hardening type. The electro-magnetic-mechanical system is modeled as a driven pendulum that impacts a mass-spring-damper system. The electromagnetic coupling effect is theoretically determined and equivalent to a nonlinear damping term. The nonlinear dynamical system is analyzed theoretically, numerically and experimentally. The results show that the bandwidth of the PEHEH is broadened than that of the energy harvester without the FUC mechanism. The maximum power reaches 26.4 mW at 4 Hz. The PEHEH can power an acceleration sensor at 4 Hz in laboratory environments and a temperature-humidity sensor in actual working conditions of an agricultural tractor's spray rod.